1. Field of the Invention
The present invention relates to an image forming apparatus and more particularly to an image forming apparatus capable of protecting an image transfer body included in an image forming section from temperature elevation.
2. Description of the Background Art
An electrophotographic color image forming apparatus including either one of a single photoconductive drum or image carrier or a plurality of photoconductive drums-arranged in tandem configuration is conventional. In a single drum type of apparatus, a plurality of developing units are arranged around the drum each for forming a toner image on the drum in a particular color. The resulting toner images of different colors are sequentially transferred from the drum to a sheet or recording medium one above the other, completing a color image on the sheet. In a tandem type of apparatus, a particular developing unit is assigned to each photoconductive drum for forming a toner image in a particular color on the drum. The resulting toner images of different colors are sequentially transferred from the drums to a sheet one above the other, also completing a color image. In the tandem type of apparatus, a fixing unit is positioned below an image transfer body in order to reduce the size of the apparatus in the direction of sheet conveyance, as taught in Japanese Patent Laid-Open Publication No. 11-224036. The tandem type of apparatus uses either one of an indirect image transfer system configured to transfer the color image to the sheet by way of an image transfer body and a direct image transfer system configured to directly transfer the toner image to the sheet being conveyed by an image transfer body.
In any case, the problem with the tandem type of apparatus is that even when, e.g., a space between the image transfer body and a fixing unit is exhausted for obstructing temperature elevation, hot air flows due to heat radiated via openings formed in the fixing unit. Such hot air is apt to heat part of the image transfer body and bring about uneven image transfer; this is the case when the toner image is directly transferred to the image transfer body. Further, it is likely that the curls of the portions of the image transfer body contacting rollers are aggravated by thermal stress. Such curls are apt to appear in the resulting image in the form of horizontal stripes when the color image is directly transferred to the image transfer body. Moreover, when the image transfer body conveys a sheet to which the color image is to be directly transferred, the former cannot stably convey the latter, also resulting in horizontal stripes mentioned above. In addition, heat effects the developing unit as well and is apt to bring about toner blocking and other problems, as known in the art.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication No. 2000-275975, 2001-154507, 2002-72833, 2002-91123 and 2003-15494.